Meet the handful of people who have bankrolled millions of dollars in advertising to influence presidential elections.

Independent groups that aren't controlled by political parties or candidates have raised more than $120 million this election cycle, according to the non-partisan Center for Responsive Politics. These outside groups probably will raise and spend many more millions on TV and radio advertising, automated phone calls, mailed brochures, Internet sites and other politicking. Total spending by them was more than $433 million during the 2004 presidential campaign.

A study by the non-profit Campaign Finance Institute says much of that money comes from just a few wealthy people.

"They are wealthy individuals who come from the top positions in our economy or are heirs to those positions, and they are the very same people who are giving major contributions to candidates and parties, and then supplementing them with these unlimited contributions," says the institute's Stephen Weissman.

Susie Tompkins Buell, co-founder of the Esprit clothing line, has given $1.3 million to outside groups since 2003.

Buell said she first got involved in Democratic politics during Bill Clinton's 1992 presidential campaign. She stays involved, in part, to help women candidates "who are really committed to supporting women's issues, like child care, health care, the environment and education."

No limits

Independent political groups multiplied after a new campaign-finance law in 2002 banned unlimited donations to political parties for their party-building efforts. Unlimited donations are allowed to two main kinds of non-profit political groups, both named after sections of the tax code governing them:

•527s must report their donors to the IRS but can raise and spend unlimited amounts.

•501(c)4s don't have to report their donors but must spend more than half of their funds for non-political purposes such as educational or social service programs.

Both Democrat Barack Obama and Republican John McCain have told their donors not to give to these groups, particularly 527s, and asked the groups not to run ads on their behalf. Obama cited potential negative 527 advertising campaigns as a reason he decided to opt out of the public-financing system for the general election.

Several top donors say they will scale back or eliminate contributions to 527s for this election. That doesn't mean big donors won't play a role in the November election.

Buell, for instance, raised more than $1 million to aid Democrat Hillary Rodham Clinton in her unsuccessful presidential bid, and more than $500,000 for the Democratic National Committee and several congressional candidates.

Motivated donors

While the big-money donors spend millions of dollars to ensure voters hear their political views, nearly all of them avoid drawing attention to themselves. Billionaire broadcasting mogul Jerry Perenchio, who has given more than $10 million to independent groups since 2003, has a list of his personal rules that begins, "Stay clear of the press. Stay out of the spotlight. It fades your suit."

The most famous example of an independent political group was Swift Boat Veterans for Truth, a 527 that ran ads in 2004 criticizing the Vietnam War record of Democratic presidential nominee John Kerry. The group questioned Kerry's command of river patrol boats in Vietnam.

Several top donors to the Swift Boat group are among the largest donors to conservative groups in the past three election cycles. They include Houston homebuilder Bob Perry, the most prolific donor to GOP-leaning groups with nearly $20 million in contributions since 2003.

A USA TODAY analysis of the top six donors to Republican- and Democratic-leaning groups over the past three federal elections found only one new major donor since 2004 among the top dozen: Casino mogul Sheldon Adelson.

Adelson, the chairman and chief executive officer of Las Vegas Sands, is a major backer of the conservative group Freedom's Watch, founded by former Bush White House officials such as press secretary Ari Fleischer to act as a counterweight to liberal groups such as MoveOn.org.

Adelson did not make any contributions to outside political groups in 2004 but has given more than $3 million to independent groups this election, records show.

None of the top 12 donors agreed to talk to USA TODAY.

Spokesmen for the independent groups say their large donors give because they believe in the groups' causes.

"They give for some of the same reasons they give to charities," David Keating of the anti-tax group Club for Growth says of his group's donors. "They also see that economic growth is very important for the future of the country, not only for the welfare of the people but for the country as a whole. That's what motivates them."